Here's one that's a couple of shades of grey.
If it was installed by'02 Code, 406.4(C)..."shall be held rigidly against the cover by more than one screw..."
If by '99 Code, 410-56(f)(3)..."shall be secured by more than one screw"....
If by '96 Code, 410-56(i) only said "Receptacles installed in raised covers shall not be secured solely by a single screw".
This installation appears to be older than the '99 Code. So it wouldn't be subject to that rule.
The box is a 4"X1-1/2" octogonal. Even if the conductors were #10, the box has the necessary volume. (I also seem to remember that in the "bad old days", there was only a 1 conductor per device deduction made from the box fill)...S
